I really need help understanding asymptotic functions and I have an exam on it in two days. I do not know how which one is little o, little omega, or theta of a function.

Here are some of the quiz questions from my professor.
1- n^2 + 500n = ___ (n lg n) - this was little omega
2- lg n^2 = ___ (lg n) - this was theta
3- lg lg n = ____(lg n) - this was little o

I dont know how why one is little omega or theta or little o. Anyone that would please explain it to me would be most appreciated. Thanks in advance.